The debilitating effects of CFS on the health of afflicted persons has been well-documented. This study broadens the scope of CFS research beyond the level of the individual to the family. Our primary purpose is to compare the fatigue study, functional performance and psychological health of children who have a parent with CFS with that of children of parents without CFS. A secondary goal is to examine the relationship between a parental CFS and a selected set of vulnerability markers in children. Perturbations in these indicators could serve as a mechanism for the inter-generational transmission of fatiguing illnesses. Probands will be married adult patients from the University of Washington Chronic Fatigue Clinic who meet diagnostic criteria for CFS and have at least one child between the ages of 10 and 17 living at home. The comparison group will be non-fatigued, married friends of CFS probands who are same sex and who have children in the same age range. All adults and children will be evaluated using a broad range of fatigue, functional performance, physical and mental health measures and selected vulnerability markers. These data will be used to address the following questions: Are children of CFS probands more likely to report high fatigue levels than children. of non-CFS probands? Are there differences in pain thresholds or cognitive functioning in the children of CFS probands? Are there higher rates of psychiatric disorders and psychosocial distress among children of CFS probands compared to children of non-CFS probands? Does having a parent with CFS impair the functioning of children and adolescents, or conversely, do the offspring of adults with CFS assume a disproportionate burden of responsibilities? For each of these questions the potential differential effects of age and sex of the proband and age, sex and pubertal status of the children will be investigated. This project elucidate several elements in our conceptual models for the pathophysiology of CFS. The examination of the effects on children of having a parent with CFS is focused on a familial predisposition to fatiguing illness. This predisposition may derive from the familial environment or genetics. Similarly, the targeted potentially pre-morbid perceptual may derive from the familial environment or genetics. Similarly, the targeted potentially pre-morbid perceptual vulnerability markers ask if there are subclinical alterations in the pain threshold and cognition of children of CFS parents; these children may be especially vulnerable for the development of fatiguing illnesses.